Optical information recording medium

ABSTRACT

An optical information recording medium includes a first dielectric protective layer, a recording layer provided on the first dielectric protective layer, including a material represented by a chemical formula of AgαInβSbγTeδ, wherein α, β, γ and δ respectively represent an atomic percent of Ag, an atomic percent of In, an atomic percent of Sb, and an atomic percent of Te, and satisfy the conditions of: 
     1≦α&lt;10, 
     1&lt;β≦20, 
     35≦γ≦70, 
     20≦δ≦35, 
     α+β+γ+δ=100, 
     4β−δ≦0, 
     γ−2δ≧0, and 
     γ−8α≧0, 
     a second dielectric protective layer provided on the recording layer, and a light reflection and heat dissipation layer provided on the second dielectric protective layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.09/199,846, filed Nov. 25, 1998, now U.S. Pat. No. 6,177,167, nowallowed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rewritable phase-change opticalinformation recording medium having a large recording capacity andcapable of rewriting information recorded therein.

2. Discussion of Background

As optical information recording media which are capable of recordinginformation therein, and from which recorded information can bereproduced or erased by the application of semi-conductor laser beamsthereto, there are conventionally known (1) a magneto-optical recordingmedium in which information can be recorded, and recorded informationcan be erased by reversing a magnetization direction of a recordinglayer thereof, utilizing heat, and (2) a phase-change opticalinformation recording medium in which information can be recorded, andrecorded information can be erased, utilizing phase changes between acrystalline phase and an amorphous phase of a recording layer thereof.

The latter phase-change optical information recording medium is capableof performing single beam overwriting, and is advantageous over otheroptical recording media in the compatibility with CD-ROM and CD-R media,so that the standardization of the phase-change optical informationrecording media as rewritable media, namely as CD-RW, has now beenestablished, and the phase-change optical information media have nowbeen commercialized.

In the meantime, large capacity storage by the phase-change opticalinformation recording media has been studied, and DVD-ROM media havebeen placed on the market. In accordance with the appearance of theDVD-ROM on the market, media called DVD-RAM are now being developed asrewritable DVD media. A DVD-RAM with a capacity of 2.6 GB will beshortly commercialized, but there is now a demand for a DVD-RAM with acapacity larger than that of ROM media.

As the materials for use in the recording layer of the phase-changeoptical information recording medium, chalcogen-based alloys, such asGe—Sb—Te, In—Sb—Te, Ge—Se—Te, Ge—Te—Bi, Sb—Se—Te, and In—Te—Au have beeninvestigated. Of these chalcogen-based alloys, Ge—Sb—Te has now reacheda level for use in practice. However, even with this Ge—Sb—Te, furtherimprovements are desired on the recording sensitivity, erasingsensitivity, and erasing ratio at overwriting.

Japanese Laid-Open Patent Applications 4-78031 and 9-263055 disclosephase-change information recording media using as recording materials inthe recording layers thereof Ag—In—Sb—Te based alloys by use of whichthe erasing ratio of the phase-change information recording media at theoverwriting is improved.

However, the repeated use overwriting characteristics of a phase-changeoptical information recording medium using the above-mentionedAg—In—Sb—Te based recording material cannot be improved by using theAg—In—Sb—Te based recording materials only, but by using upper and lowerprotective layers, and a heat dissipation layer which are overlaid.

As the materials for such protective layers, ZnS.SiO₂ as disclosed inJapanese Patent Publication 7-114031, metallic oxides, metallic sulfidesand metallic nitrides, and mixtures thereof are conventionally proposed.However, the improvement of the repeated use overwriting characteristicsof the phase-change optical information recording medium is stillinsufficient for use in practice.

As mentioned above, the phase-change optical information recording mediahave now been commercialized as CD-RW. The CD-RW is used as an externalmemory device for use with personal computers. Recently DVD-ROM playersare placed on the market, so that there is a great demand for largecapacity, rewritable DVD media.

The DVD-RAM which has now been commercialized as rewritable DVD mediumhas a capacity of 2.6 GB, and recording and reproduction is conducted ata linear speed of about 6 m/sec, while in DVD-ROM, the linear speed forrecording and reproduction is about 3.5 m/sec, and the capacity ofDVD-ROM is 4.7 GB. It is required that rewritable DVD media have acapacity greater than that of ROM, be capable of performing recordingand reproduction at a speed of two times greater than that of ROM, andbe compatible with ROM. In order to meet such requirements, it isstrictly required that the DVD media have a high line density, a lowjitter, and a large overwriting repetition number. In particular, theimprovement of the overwriting repetition number is one of mostsignificant targets to be cleared in the phase-change opticalinformation recording media in order to enhance the performancereliability of the media. The Ag—In—Sb—Te based phase-change recordingmaterials are suitable for high density recording, so that how toimprove the overwriting repetition characteristics thereof is still asignificant target to be cleared.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide anAg—In—Sb—Te based phase-change optical information recording medium withhigh overwriting repetition number, high recording density, excellentrecording and reproduction characteristics capable of attaining highspeed recording and reproduction.

A second object of the present invention to provide a heat dissipationlayer and a protective layer for use in the above-mentioned opticalinformation recording medium of the present invention in order to attainthe above object of the present invention, in particular, high speedrecording and reproduction.

The first and second objects of the present invention can be achieved byan optical information recording medium comprising:

a first dielectric protective layer,

a recording layer provided on said first dielectric protective layer,comprising a material represented by a chemical formula of AgαInβSbγTeδ,wherein α, β, γ and δ respectively represent an atomic percent of Ag, anatomic percent of In, an atomic percent of Sb, and an atomic percent ofTe, and satisfy the conditions of:

1≦α<10,

1<β≦20,

35≦γ≦70,

20≦δ≦35,

α+β+γ+δ=100,

4β−δ≦0,

γ−2δ≧0, and

γ−8α≧0,

a second dielectric protective layer provided on said recording layer,and

a light reflection and heat dissipation layer provided on said seconddielectric protective layer.

The above-mentioned optical information recording medium may furthercomprise a heat dissipation layer which is interposed between the seconddielectric protective layer and the light reflection and heatdissipation layer, the heat dissipation layer comprising a materialwhich comprises Mg, In and O, with the atomic ratios of Mg and Insatisfying a formula of 0.60<In /(In+Mg)<1.0.

Furthermore, in the above-mentioned optical information recording medium, it is preferable that the heat dissipation layer and the seconddielectric protective layer respectively have a thickness of D1 and athickness of D2, with a ratio of D1:D2 being in a range of (10:90) to(50:50).

It is also preferable that in the above-mentioned optical informationrecording medium, the heat dissipation layer have a refractive index of1.9 to 2.1.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

The single FIGURE is a schematic cross-sectional view of an example ofan optical information recording medium of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying Single FIGURE, an example of anoptical information recording medium of the present invention will nowbe explained.

In the FIGURE, reference numeral 1 represents a substrate; referencenumeral 2, a first dielectric protective layer; reference numeral 3, arecording layer; reference numeral 4, a second dielectric protectivelayer; reference numeral 5, a heat dissipation layer; reference numeral6, a light reflection and heat dissipation layer; and reference numeral7, an organic environment protective layer. Each of the above layers,for example, the heat dissipation layer 5 may be composed of twooverlaid layers.

Specific examples of the materials for use in the first and seconddielectric protective layers 2 and 4 are metallic oxides such asSiO_(x), ZnO, SnO₂, Al₂O₃, TiO₂, In₂O₃, MgO, ZrO₂ and Ta₂O₅; nitridessuch as Si₃N₄, AlN, TiN, BN and ZrN; sulfides such as ZnS and TaS₄;carbides such as SiC, TaC, B₄C, WC, TiC and ZrC. These materials can beused either in the form of a simple body or in the form of a mixture.Examples of the mixtures are a mixture of ZnS and SiO_(x) and a mixtureof Ta₂O₅ and SiO_(x). Each of the above-mentioned materials is suitablefor use in the first and second dielectric protective layers 2 and 4with respect to the physical properties thereof, such as thermalconductivity, specific heat, coefficient of thermal expansion,refractive index, and adhesion to materials for the substrate and/or therecording layer, and has advantages over other materials, particularlywith respect to high melting point, high thermal conductivity, and lowcoefficient of thermal expansion and excellent adhesion to the materialsfor the substrate and/or the recording layer. In particular, thecharacteristics of the second dielectric protective layer havesignificant effects on the overwriting repetition number and thesensitivity of the optical information recording material.

With respect to the above-mentioned protective layers, a layer thicknessis an important factor which has significant effects on the performanceof the optical information recording material.

It is preferable that the first dielectric protective layer 2 have athickness in the range of 50 to 250 nm, more preferably in the range of75 to 200 nm. When the thickness of the first dielectric protectivelayer 2 is less than 50 nm, a protection effect from the environmentconditions, a heat resistant effect, and a heat accumulation effect tendto be lowered, while when the thickness of the first dielectricprotective layer 2 is more than 250 nm, the first protective layer 2tends to be peeled away or cracked when the temperature thereof isincreased in the course of the formation of the first protective layer 2by sputtering or the like, and when such peeling or cracking takes placein the first dielectric protective layer 2, the recording sensitivity ofthe optical information recording material tends to be lowered.

It is preferable that the second dielectric protective layer 4 have athickness in the range of 10 to 100 nm, more preferably in the range of15 to 50 nm. When the thickness of the second dielectric protectivelayer 4 is less than 10 nm, the heat resistance effect thereof tends tobe lowered, when the thickness exceeds 100 nm, the overwritingrepetition characteristics of the optical information recording mediumtend to be impaired because of the lowering of the recording sensitivityof the optical information recording medium, the peeling away and thedeformation of the second dielectric protective layer 4 by the elevationof the ambient temperature, and the lowering of the heat dissipationcharacteristics thereof.

Specific examples of the materials for the light reflection and heatdissipation layer 6 include metals such as Al, Au, Cu, Ag, Cr, Sn, Zn,In, Pd, Zr, Fe, Co, Ni, Si, Ge, Sb, Ta, W, Ti and Pb, alloys thereof,and mixtures thereof. When necessary, the light reflection and heatdissipation layer 6 may be composed of a plurality of overlaid layers,for instance, each comprising a different metal or alloy, or a mixtureof a different metal or a different alloy, or a mixture a differentmetal and a different alloy.

The light reflection and heat dissipation layer 6 is an important layerfor effectively dissipating heat.

It is preferable that the light reflection and heat dissipation layer 6have a thickness in the range of 30 to 250 nm, more preferably in therange of 50 to 150 nm.

When the light reflection and heat dissipation layer 6 is too thick, theheat dissipation effect becomes so high that the sensitivity of theoptical information recording medium tends to be lowered, while when thelight reflection and heat dissipation layer 6 is too thin, thesensitivity of the optical information recording medium become good, butthe overwriting repetition characteristics of the optical informationrecording medium tend to be impaired. It is required that the lightreflection and heat dissipation layer 6 have high thermal conductivity,high melting point and good adhesiveness to the materials of the layersadjacent thereto.

It is preferable that the heat dissipation layer 5 comprise an Mg—In—Obased oxide, with a ratio of In/(In+Mg) being in the range of 0.60 to1.0. It is more preferable that the Mg—In—O based oxide have aresistivity of 10⁻⁴ Ω·cm or less. The Mg—In—O based oxide is preferablefor use in the heat dissipation layer 5 because of its high meltingpoint. The above-mentioned range of 0.60 to 1.0 in terms of In/(In+Mg)corresponds to a mixture of 1 mole of In₂O₃ and not more than 0.40 molesof MgO.

A thin film of In₂O₃ has high light transmittance, but is not consideredto have a sufficiently low resistivity. MgO is not suitable for massproducing a thin film thereof because of too low the film formationspeed thereof to perform the mass production thereof. It is preferablethat In/(In+Mg) being in the range of 0.8 to 0.9.

The Mg—In—O based oxide has high electroconductivity when the ratio ofIn/(In+Mg) is in the range of 0.60 to 1.0 and has a refractive index ofabout 2. Therefore, the Mg—In—O based oxide contains MgO having a highmelting point and has a light transmittance of 80%, so that when theMg—In—O based oxide is used in the heat dissipation layer 5, the heatdissipation layer 5 has a higher thermal conductivity than that of thesecond dielectric protective layer 2.

It is preferable that the heat dissipation layer 5 have a refractiveindex in the range of 1.9 to 2.1 so as to have substantially the samerefractive index as that of the second dielectric protective layer 4.

It is preferable that the ratio of the thickness of the seconddielectric protective layer 4 composed of ZnS.SiO₂ to the thickness ofthe heat dissipation layer 5 composed of the MgO—In₂O₃ based material beoptimized. This ratio becomes more important as the line density and thelinear speed are increased. In this case, a large power is requiredsince the recording frequency is increased and accordingly the laserpulse width is narrowed at the time of recording. However, when thepower is increased, the temperature is accordingly elevated, so thatheat accumulates, the overwriting repetition number decreases, the edgesof recording marks blur, the recording marks are shifted in position,with improper jittering.

In order to have the layer thickness ratio optimizing effect exhibitwhen the heat dissipation layer 5 composed of the Mg—In—O based oxideand the second dielectric protective layer 4 composed of ZnS.SiO₂ areoverlaid, it is preferable that the ratio of the thickness of the seconddielectric protective layer 4: the thickness of the heat dissipationlayer 5 be in the range of (50:50) to (90:10), more preferably in therange of (60:40) to (80:20). In the case where the heat dissipationlayer 5 is thicker than the second dielectric protective layer 4 , heataccumulation is difficult to be performed, so that the sensitivity andjittering performance of the optical information recording medium areimpaired. When a excessively thin heat dissipation layer does notexhibit sufficient heat dissipation effect.

Recording is performed in the optical information recording mediumcomposed of the above-mentioned materials, with the application of asemiconductor laser beam with a wavelength of 635 nm, using an NA 0.6pickup, and reproduction is performed in the above optical informationrecording medium with the application of a semiconductor laser with awavelength of 650 nm, using an NA 0.6 pickup. The recording method isconducted, using a pulse width modulation system with a modulation codeof EFM+[8/16, RLL(2,10)].

Other features of this invention will become apparent in the course ofthe following description of exemplary embodiments, which are given forillustration of the invention and are not intended to be limitingthereof.

EXAMPLE 1

A substrate made of polycarbonate with a thickness of 0.6 mm, a trackpitch of 0.74 μm, and a groove with a width of 0.45 μm and a depth of 50nm was subjected to a dehydration processing at 70 to 80° C.

A first dielectric protective layer with a thickness of 170 nm wasformed on the above substrate by sputtering, using a ZnS.SiO₂ target.

A recording layer with a thickness of 18 nm was formed on the abovefirst dielectric protective layer by sputtering, using an AgInSbTetarget with a composition as shown in Example 1 in TABLE 1, at an argongas pressure of 3×10⁻³ torr, with a RF power of 300 W.

A second dielectric protective layer with a thickness of 170 nm wasformed on the above recording layer by sputtering, using a ZnS.SiO₂ inthe same manner as with the above-mentioned first dielectric protectivelayer.

A light reflection and heat dissipation layer made of an AlTi alloylayer with a thickness of 120 nm was formed on the above seconddielectric protective layer by sputtering.

Finally, a protective layer made of an ultraviolet curing resin film wasformed by coating on the above light reflection and heat dissipationlayer, whereby an optical information recording medium No. 1 of thepresent invention was fabricated.

After the above fabrication of the optical information recording mediumNo. 1, the recording layer thereof was in an amorphous state, so thatthe optical information recording medium No. 1 was initialized bycrystallizing the recording layer.

Recording was performed the application of a semiconductor laser beamwith a wavelength (λ) of 635 nm to the optical information recordingmedium No. 1, using an NA 0.6 pickup, using the pulse width modulationsystem with a modulation code of EFM+[8/16, RLL(2,10)]. The linear speedat the time of recording and reproduction was varied in the range of 3.5m/sec to 7 m/sec in accordance with the composition of the recordinglayer. The ratio of the recording power/the erasing power was set in therange of about 2 to 2.2, and the recording was conducted with a bottompower set at the same as or below the reproduction power. The recordingpower was applied up to 15 mW (maximum). Recording was conducted in thegroove of the optical information recording medium No. 1 with therecording frequency for the recording set in the range of 23.3 MHz to46.6 MHz. Furthermore, a data to clk jitter was measured for thespecific composition of the recording layer by performing the recordingand the reproduction.

Furthermore, the recording was performed with an optimum recording powerat which the jitter σ/Tw (Tw: window width) was minimized. Thisrecording was repeated to perform the overwriting. The overwritingrepetition number shown in TABLE 1 is the number at which the jitter was10% or less.

EXAMPLES 2 to 9

The same procedure as in Example 1 was repeated except that thecomposition of the recording layer was changed as shown in TABLE 1,whereby optical information recording media No. 2 to No. 9 of thepresent invention were fabricated and the overwriting repetition numberof each of the optical information recording media No. 2 to No. 9 wasmeasured in the same manner as in Example 1. The results are shown inTABLE 1.

COMPARATIVE EXAMPLES 1 to 16

The same procedure as in Example 1 was repeated except that thecomposition of the recording layer was changed as shown in TABLE 2,whereby comparative optical information recording media No. 1 to No. 16were fabricated and the overwriting repetition number of each of thecomparative optical information recording media No. 1 to No. 16 wasmeasured in the same manner as in Example 1. The results are shown inTABLE 2.

The results shown in TABLE 1 and TABLE 2 indicate that the opticalinformation recording media No. 1 to No. 9 of the present inventionshown in TABLE 1 are capable of attaining significantly higheroverwriting repetition numbers and accordingly better performancereliability than those attained by the comparative optical informationrecording media No. 1 to No. 16 shown in TABLE 2.

EXAMPLE 10

A substrate made of polycarbonate with a thickness of 0.6 mm, a trackpitch of 1.48 μm, and a groove with a width of 0.74 μm and a depth of 65nm was subjected to a dehydration processing at high temperature.

A first dielectric protective layer with a thickness of 170 nm wasformed on the above substrate by sputtering, using a ZnS.SiO₂ target.

A recording layer with a thickness of 18 nm was formed on the abovefirst dielectric protective layer by sputtering, using an AgInSbTetarget with the same composition as in Example 1 as shown in TABLE 1, ata mixed gas pressure of 3×10⁻³ torr, with a flow of 0.5 sccm of a mixedgas of argon and nitrogen gasses, with a RF power of 300 W.

A second dielectric protective layer with a thickness of 170 nm wasformed on the above recording layer by sputtering, using a ZnS.SiO₂ inthe same manner as with the above-mentioned first dielectric protectivelayer.

A heat dissipation layer comprising a Mg—In—O oxide based material,having a refractive index of about 2.1, with a thickness of 250 nm, withthe ratio of the thickness of the second dielectric protective layer tothe thickness of the heat dissipation layer being 50:50, and with anIn/(In+Mg) ratio of 0.96, was formed on the second dielectric protectivelayer.

A light reflection and heat dissipation layer made of an AlTi alloylayer with a thickness of 120 nm was formed on the above heatdissipation layer by sputtering.

Finally, a protective layer made of an ultraviolet curing resin film wasformed on the above light reflection and heat dissipation layer, wherebyan optical information recording medium No. 10 of the present inventionwas fabricated.

Recording was performed with the application of a semiconductor laserbeams with a wavelength (λ) of 635 nm, using an NA 0.6 pickup, using thepulse width modulation system with a modulation code of EFM+[8/16,RLL(2,10)]. The ratio of the recording power/the erasing power was setin the range of about 2 to 2.2, and the reproduction power was set at 1mW. The recording was conducted in the groove of the optical informationrecording medium No. 10 with a bottom power set at the same as or belowthe reproduction power. With the linear speed set at 3.5 m/sec and therecording frequency set at 23.3 MHz, the recording was conducted.Overwriting was repeated with a recording power at which the jitter wasminimized. As the jitter, a data to clk jitter was measured.

EXAMPLES 11 to 14

The same procedure as in Example 10 was repeated except that the ratioof the thickness of the second dielectric protective layer to thethickness of the heat dissipation layer was changed as shown in TABLE 3,whereby optical information recording media No. 11 to No. 14 of thepresent invention were fabricated, and the overwriting repetition numberof each of the optical information recording media No. 11 to No. 14 wasmeasured. The results are shown in TABLE 3.

COMPARATIVE EXAMPLE 17

The same procedure as in Example 10 was repeated except the compositionof the recording layer was changed to the same composition of therecording layer as in Comparative Example 5, and that and the In/(In+Mg)ratio was changed to 0.98, whereby a comparative optical informationrecording medium No. 17 was fabricated, and the overwriting repetitionnumber of the comparative optical information recording medium No. 17was measured. The results are shown in TABLE 3.

COMPARATIVE EXAMPLE 18

The same procedure as in Comparative Example 17 was repeated except thatthe ratio of the thickness of the second dielectric protective layer tothe thickness of the heat dissipation layer was changed as shown inTABLE 3, whereby a comparative optical information recording medium No.18 was fabricated, and the overwriting repetition number of the opticalinformation recording medium No. 18 was measured. The results are shownin TABLE 3.

The results shown in TABLE 3 indicate that the overwriting repetitionnumber is optimized when the composition of the recording layer, theIn/(In+Mg) ratio, and the ratio of the thickness of the seconddielectric protective layer to the thickness of the heat dissipationlayer are in the respective ranges as defined in the present invention.The overwriting repetition number shown in TABLE 3 is also the number atwhich the jitter was 10% or less.

TABLE 1 Over- writing Ag In Sb Te Repetition No. α β γ δ 4β − δ ≦ 0 γ −2δ ≧ 0 γ − 8α ≧ 0 Number Ex. 1 3.8 7.0 61.0 28.2  −0.2 4.6 30.6 10000Ex. 2 4.0 3.0 63.6 29.4 −17.4 4.8 31.6 50000 Ex. 3 4.6 6.0 60.0 29.4 −5.4 1.2 23.2 30000 Ex. 4 6.0 4.0 63.0 27.0 −11.0 9.0 15.0 40000 Ex. 55.6 4.0 64.0 26.4 −10.4 11.2  19.2 40000 Ex. 6 4.0 3.0 62.4 30.6 −18.61.2 30.4 45000 Ex. 7 4.0 3.0 65.4 27.6 −15.6 10.2  33.4 55000 Ex. 8 5.04.4 62.0 28.6 −11.0 4.8 22.0 60000 Ex. 9 6.2 5.2 60.6 28.0  −7.2 4.611.0 35000

TABLE 2 Over- writing Ag In Sb Te Repetition No. α β γ δ 4β − δ ≦ 0 γ −2δ ≧ 0 γ − 8α ≧ 0 Number Comp. 3.8 11.8 62.4 22.0 25.2 18.4 32.0 3000Ex. 1 Comp. 3.2  9.7 63.3 23.8 15.0 15.7 37.7 5000 Ex. 2 Comp. 2.8 10.061.8 25.4 14.6 11.0 39.4 3000 Ex. 3 Comp. 6.0  8.0 59.0 27.0  5.0  5.011.0 3000 Ex. 4 Comp. 5.6  7.5 60.5 26.4  3.6  7.7 15.7 7000 Ex. 5 Comp.9.0  6.0 59.0 26.0 −2.0  7.0 −13.0  9000 Ex. 6 Comp. 3.6 11.0 58.4 27.017.0  4.4 29.6 1000 Ex. 7 Comp. 1.5 10.0 60.5 28.0 12.0  4.5 48.5 1000Ex. 8 Comp. 3.8  9.5 59.0 27.6 10.4  3.8 28.6  900 Ex. 9 Comp. 3.6 12.059.0 25.4 22.6  8.2 30.2  500 Ex. 10 Comp. 5.6 10.8 57.2 26.4 16.8  4.412.4  300 Ex. 11 Comp. 4.1 12.3 53.4 30.2 19.0 −7.0 20.6  100 Ex. 12Comp. 3.4 10.2 55.0 31.4  9.4 −7.8 27.8  100 Ex. 13 Comp. 8.0  8.0 57.027.0  5.0  3.0 −7.0  700 Ex. 14 Comp. 6.0  9.0 59.0 26.0 10.0  7.0 11.01000 Ex. 15 Comp. 3.6 11.5 58.4 27.5 18.5  3.4 29.6  900 Ex. 16

TABLE 3 Layer Thickness Ratio of Heat Second Dissipa- Dielectric Over-Second tion Protective writing Dielectric Layer Layer to Heat Repeti-Composition Protective In/(In + Dissipation tion of Recording Layer Mg)Layer Number Layer Ex. 10 ZnS · SiO₂ 0.96 50:50 10000 Same as in Ex. 1Ex. 11 ZnS · SiO₂ 0.96 60:40 15000 Same as in Ex. 1 Ex. 12 ZnS · SiO₂0.96 70:30 20000 Same as in Ex. 1 Ex. 13 ZnS · SiO₂ 0.96 80:20 30000Same as in Ex. 1 Ex. 14 ZnS · SiO₂ 0.96 90:10 20000 Same as in Ex. 1Comp. ZnS · SiO₂ 0.98 50:50  7500 Same as in Ex. 17 Comp. Ex. 5 Comp.ZnS · SiO₂ 0.98 60:40  9000 Same as in Ex. 18 Comp. Ex. 5

Japanese Patent Application No. 09-347175 filed Dec. 2, 1997 is herebyincorporated by reference.

What is claimed is:
 1. An optical information recording mediumcomprising: a first dielectric protective layer, a recording layerprovided on said first dielectric protective layer, comprising amaterial represented by a chemical formula of AgαInβSbγTeδ, wherein α,β, γ and δ respectively represent an atomic percent of Ag, an atomicpercent of In, an atomic percent of Sb, and an atomic percent of Te, andsatisfy the conditions of: 1≦α<10, 1<β≦7, 35≦γ≦70, 20≦δ≦35, α+β+γ+δ=100,4β−δ≦0, γ−2δ≧0, and γ−8α≧0, a second dielectric protective layerprovided on said recording layer, and a light reflection and heatdissipation layer provided on said second dielectric protective layer.